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# Improving compiler diagnostics with Overlays
Jeff Trull (he/him) - Pronunciation: rhymes with "hull" and "dull", IRC: jaafar, @jaafar@hachyderm.io

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Overlays are a feature of Emacs that allow changing the
appearance of text while preserving its contents. They play a prominent
role in packages like org-mode, which uses them to hide or reveal custom
properties and display inline images, and magit, which uses them to
highlight diffs.

The presenter will give a introduction to the features of overlays,
demonstrating how to:

-   Create and use overlays in Emacs Lisp code
-   Query locations in an existing buffer to find out what overlays are
present.

He will then demonstrate a new compilation minor mode for improving the
readability of error messages, using overlays to flexibly reformat portions
of the compiler output under user control.



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